1. Field
The present invention relates to a method, system, and article of manufacture for managing processing systems access to control blocks providing information on storage resources.
2. Description of the Related Art
In certain computing environments, multiple host systems may communicate with multiple control units (CUs) (also known as storage controllers, storage subsystems, enterprise storage servers, etc.) providing access to storage devices, such as interconnected hard disk drives through one or more logical paths. The interconnected drives may be configured as a Direct Access Storage Device (DASD), Redundant Array of Independent Disks (RAID), Just a Bunch of Disks (JBOD), etc. The control unit may configure one or more logical subsystems (LSSs), where each LSS may be configured to include multiple volumes.
The host system may include a channel subsystem that maintains information to access volumes in an LSS in the control unit. The channel subsystem includes subchannels, which provides state tracking for the execution of the I/O operations for the channel subsystem and provides information on paths connecting the host to a volume in an LSS. The host operating system maintains a unit control block (UCB) providing information on a base unit address assigned to one volume and the subchannel that the channel subsystem uses to access the volume on the base device. The channel subsystem is aware of individual subchannels and the paths they have. The host initiates an I/O operation toward a volume by initiating a channel program which consists of a series of I/O instructions, such as a chain of channel command word (CCW) commands, at the subchannel.
Processing systems executing in a host may access a UCB to use to access the volume represented by the UCB. In the Z/OS® operating system from International Business Machines Corporation (“IBM”®), the processing systems may access a UCB by issuing a CAPTURE command to obtain a copy of the UCB, then issuing a PIN command to pin the captured UCB to prevent other processing systems from modifying or deleting the UCB. Any processing system with an interest in a UCB or a captured copy of a UCB should PIN the UCB. The information in captured UCB copies will become invalid if the actual UCB is altered or deleted during change activities such as a dynamic ACTIVATE of an Input/Output Definition File (IODF). PIN-ing CAPTURED UCBs prevents the information in the UCB copy from being altered or deleted. (IBM and Z/OS are trademarks of IBM in the United States and other countries.)
There is a need in the art for improved techniques for managing control blocks, such as UCBs, being accessed by different processing systems.